The present invention relates generally to X-ray tubes, and more particularly, to lubricant sealing within X-ray tube bearing assemblies.
Various techniques for manufacturing a rotary anode type X-ray tube are known. The rotary anode type X-ray tube typically includes generally, a vacuum chamber, a rotating shaft and a stator. A bearing cartridge also typically is provided between the rotating shaft and the stator and includes a roller type bearing assembly. The rotating shaft is attached to the anode that is rotated using the shaft. The anode includes a target that heats to high temperatures during the operation of the X-ray tube. This is due to the constant impingement of electrons on the surface of the target-bearing cartridge, which accumulates heat generated at the target. As a result, there is a temperature inequality between the rotating shaft and the stator. This causes increased wear and tear of the X-ray tube, which can result in reduced performance.
A lubricant is typically provided in the bearing cartridge to reduce the heat level, wear and thereby increase the life of the bearing. The lubricant equalizes the temperatures of the shaft and the stator. Both solid as well as liquid metal lubricants are used to surround the bearing assembly and increase their conductivity. X-ray tubes containing bearing cartridges, which use liquid metal lubricants (e.g., Gallium or Gallium alloys) typically have a longer life and reduced operation noise at higher gantry loads and at higher anode rotation speeds. However, an appropriate sealing arrangement must be provided to reduce or eliminate the risk of the liquid metal lubricant leaking from the bearing section into the vacuum chamber. Such leakage can cause electrical (high voltage) instability in the X-ray tube, thereby shortening operating life.
In known X-ray tubes, a seal is provided in the form of an axial interface between the liquid metal lubricant and the vacuum chamber, to prevent this leakage. However, the axial interface may not perform adequately at higher loads and speeds.